It has been shown, in the above-referenced co-pending application, that microwave energy can effectively be used to create beneficial histological changes in subdermal, dermal and superficial features, such as blood vessels, skin, wrinkles and hair in the human body. By properly balancing the intensity and total energy applied to a limited surface area, the microwave energy penetrates to a chosen depth and interacts in a manner to effect the desired changes without harm or trauma to the patient. For example, a subdermal skin condition, commonly referred to as spider veins, (telangiectasia) is treatable by energy dosages which penetrate through the dermis to heat localized subdermal areas to above a critical temperature, such as in excess of 60.degree. C. The localized temperature increase causes inflammation of vessel walls, subsequently blocking blood flow and impelling the creation of new blood flow paths, thus eliminating the appearance of spider veins. Other subdermal conditions such as varicose veins, which involve larger, deep tissue vessels, can also be treated because of the penetrating character of the microwave energy. Similarly, collagen tissue and adipose deposits may be treated by microwaves using the same principles. The aspect being treated may also be primarily a surface condition, such as wrinkles, stretch marks, cellulite, warts or dermal lesions.
Depilation is a related application in which microwave energy has been found to be particularly useful. For effective depilation the energy penetrates to reach follicular matrices and papillae, attacking the base of hair follicles and minimizing hair regrowth.
Microwave wavelengths are selected such that the wave energy preferentially interacts with the targeted tissues, such as blood or vessel walls, to enhance the localized effects of the treatment. Energy doses are kept within a range suitable for both safety and patient comfort.
Laser energy, which is widely used for similar purposes, is at much shorter wavelengths which penetrate organic matter much less effectively, and heat by absorption in superficial tissues or hair, but only when the target has the needed light responsive characteristics. Heat is then transferred from the impinged surface into a subdermal or deep tissue area to effect a histological change. The laser energy can be intensified, in order to penetrate more deeply, but still is significantly attenuated and also is much more likely to cause skin burns. For depilation treatments, laser energy must impinge upon light absorptive pigmentation in exposed hair and rely on the side effect of heat transfer to attack the follicular matrices. Light reflection and light rejection at less densely pigmented tissues and follicles diminishes the amount of useful energy, thereby making laser treatment inefficient for such targets. Skin resurfacing treatments, based upon radiative effects on collagen and adipose tissues, for example, are also more efficient where wave energy reaches the target tissue with little attenuation.
In these treatment systems, as described in the above referenced application, discrete surface targets are selected and radiated with microwave energy until a target feature or area peripheral to the target area has been excited with energy of chosen intensity and duration. Since a wide beam delivering heating energy to a broad area could undesirably affect non-target regions, energy application should be with a device having a small transmitting end which delivers a narrow energy beam. Because the concentration of electromagnetic wave energy is highest immediately adjacent the transmitting source, the skin surface adjacent the source is cooled so as to minimize overheating, discomfort and trauma. Various expedients for this purpose include use of a cooled, thermally conductive member in contact with the skin, cooling of the skin by expanding a pressurized coolant directed against the skin, and pre-cooling the skin with a frigid element or liquid. It is essential that such sources be used in timed relation to the application of wave energy from the applicator, and that the cooling not interfere with or diminish the applied energy. Moreover, the thermal transfer dynamics should preferably be complementary to the microwave energy application, in terms of time of delivery, thermal gradient in the tissues, and the temperature levels that are maintained.
Further, the energy applicator should not impair viewing by the doctor or technician, or occlude the target area, but should preferably permit clear visualization along with precise placement of the applicator at the target surface. The cross-sectional area of the transmitting end of the device, therefore, must be relatively small, and appropriately sized in relation to the target area to be treated. The minimum cross-sectional emitter area is determined by the wavelength chosen and the overall size and mass also have to be suitable for manual handling of the unit. The power level of the energy (watts) and the energy concentration (joules/cm.sup.2) that are to be used must also be accommodated in the design of the device. The prior application referenced above has disclosed how the cross-sectional area of the emitter end of the device can be reduced by incorporating dielectric materials. The device must not only be compact, but it should be ergonomically designed for easiest placement and actuation, so that a relatively large target area can be covered by successive applications without redundancy. In addition, the dangers of erroneous energization, excessive exposure, and improper sequencing should be minimized in ways that free the operator from responsibilities for safeguards to the extent possible.